Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S969380AbdI0ATR (ORCPT ); Tue, 26 Sep 2017 20:19:17 -0400 Received: from mail-wm0-f50.google.com ([74.125.82.50]:49621 "EHLO mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S968526AbdI0ATP (ORCPT ); Tue, 26 Sep 2017 20:19:15 -0400 X-Google-Smtp-Source: AOwi7QBTN4HfrN/QJrCn9Aw+qPGWDE5xcb5YNaA+1bBA85fyfA35DqcVcEh32Xf/lWf1oKFITT7bxw7gbr1MBrzISZc= MIME-Version: 1.0 In-Reply-To: References: <20170921014620.GA20906@castle> <20170926131011.GB26395@castle.DHCP.thefacebook.com> From: Yuchung Cheng Date: Tue, 26 Sep 2017 17:18:32 -0700 Message-ID: Subject: Re: [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp_input.c To: Roman Gushchin Cc: Oleksandr Natalenko , Hideaki YOSHIFUJI , Alexey Kuznetsov , netdev , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id v8R0JVkF030018 Content-Length: 8059 Lines: 132 On Tue, Sep 26, 2017 at 5:12 PM, Yuchung Cheng wrote: > On Tue, Sep 26, 2017 at 6:10 AM, Roman Gushchin wrote: >>> On Wed, Sep 20, 2017 at 6:46 PM, Roman Gushchin wrote: >>> > >>> > > Hello. >>> > > >>> > > Since, IIRC, v4.11, there is some regression in TCP stack resulting in the >>> > > warning shown below. Most of the time it is harmless, but rarely it just >>> > > causes either freeze or (I believe, this is related too) panic in >>> > > tcp_sacktag_walk() (because sk_buff passed to this function is NULL). >>> > > Unfortunately, I still do not have proper stacktrace from panic, but will try >>> > > to capture it if possible. >>> > > >>> > > Also, I have custom settings regarding TCP stack, shown below as well. ifb is >>> > > used to shape traffic with tc. >>> > > >>> > > Please note this regression was already reported as BZ [1] and as a letter to >>> > > ML [2], but got neither attention nor resolution. It is reproducible for (not >>> > > only) me on my home router since v4.11 till v4.13.1 incl. >>> > > >>> > > Please advise on how to deal with it. I'll provide any additional info if >>> > > necessary, also ready to test patches if any. >>> > > >>> > > Thanks. >>> > > >>> > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=195835 >>> > > [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__www.spinics.net_lists_netdev_msg436158.html&d=DwIBaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=jJYgtDM7QT-W-Fz_d29HYQ&m=MDDRfLG5DvdOeniMpaZDJI8ulKQ6PQ6OX_1YtRsiTMA&s=-n3dGZw-pQ95kMBUfq5G9nYZFcuWtbTDlYFkcvQPoKc&e= >>> > >>> > We're experiencing the same problems on some machines in our fleet. >>> > Exactly the same symptoms: tcp_fastretrans_alert() warnings and >>> > sometimes panics in tcp_sacktag_walk(). >>> > >>> > Here is an example of a backtrace with the panic log: >> >> Hi Yuchung! >> >>> do you still see the panics if you disable RACK? >>> sysctl net.ipv4.tcp_recovery=0? >> >> No, we haven't seen any crash since that. > I am out of ideas how RACK can potentially cause tcp_sacktag_walk to > take an empty skb :-( Do you have stack trace or any hint on which call > to tcp-sacktag_walk triggered the panic? internally at Google we never > see that. hmm something just struck me: could you try sysctl net.ipv4.tcp_recovery=1 net.ipv4.tcp_retrans_collapse=0 and see if kernel still panics on sack processing? > > >> >>> >>> also have you experience any sack reneg? could you post the output of >>> ' nstat |grep -i TCP' thanks >> >> hostname TcpActiveOpens 2289680 0.0 >> hostname TcpPassiveOpens 3592758 0.0 >> hostname TcpAttemptFails 746910 0.0 >> hostname TcpEstabResets 154988 0.0 >> hostname TcpInSegs 16258678255 0.0 >> hostname TcpOutSegs 46967011611 0.0 >> hostname TcpRetransSegs 13724310 0.0 >> hostname TcpInErrs 2 0.0 >> hostname TcpOutRsts 9418798 0.0 >> hostname TcpExtEmbryonicRsts 2303 0.0 >> hostname TcpExtPruneCalled 90192 0.0 >> hostname TcpExtOfoPruned 57274 0.0 >> hostname TcpExtOutOfWindowIcmps 3 0.0 >> hostname TcpExtTW 1164705 0.0 >> hostname TcpExtTWRecycled 2 0.0 >> hostname TcpExtPAWSEstab 159 0.0 >> hostname TcpExtDelayedACKs 209207209 0.0 >> hostname TcpExtDelayedACKLocked 508571 0.0 >> hostname TcpExtDelayedACKLost 1713248 0.0 >> hostname TcpExtListenOverflows 625 0.0 >> hostname TcpExtListenDrops 625 0.0 >> hostname TcpExtTCPHPHits 9341188489 0.0 >> hostname TcpExtTCPPureAcks 1434646465 0.0 >> hostname TcpExtTCPHPAcks 5733614672 0.0 >> hostname TcpExtTCPSackRecovery 3261698 0.0 >> hostname TcpExtTCPSACKReneging 12203 0.0 >> hostname TcpExtTCPSACKReorder 433189 0.0 >> hostname TcpExtTCPTSReorder 22694 0.0 >> hostname TcpExtTCPFullUndo 45092 0.0 >> hostname TcpExtTCPPartialUndo 22016 0.0 >> hostname TcpExtTCPLossUndo 2150040 0.0 >> hostname TcpExtTCPLostRetransmit 60119 0.0 >> hostname TcpExtTCPSackFailures 2626782 0.0 >> hostname TcpExtTCPLossFailures 182999 0.0 >> hostname TcpExtTCPFastRetrans 4334275 0.0 >> hostname TcpExtTCPSlowStartRetrans 3453348 0.0 >> hostname TcpExtTCPTimeouts 1070997 0.0 >> hostname TcpExtTCPLossProbes 2633545 0.0 >> hostname TcpExtTCPLossProbeRecovery 941647 0.0 >> hostname TcpExtTCPSackRecoveryFail 336302 0.0 >> hostname TcpExtTCPRcvCollapsed 461354 0.0 >> hostname TcpExtTCPAbortOnData 349196 0.0 >> hostname TcpExtTCPAbortOnClose 3395 0.0 >> hostname TcpExtTCPAbortOnTimeout 51201 0.0 >> hostname TcpExtTCPMemoryPressures 2 0.0 >> hostname TcpExtTCPSpuriousRTOs 2120503 0.0 >> hostname TcpExtTCPSackShifted 2613736 0.0 >> hostname TcpExtTCPSackMerged 21358743 0.0 >> hostname TcpExtTCPSackShiftFallback 8769387 0.0 >> hostname TcpExtTCPBacklogDrop 5 0.0 >> hostname TcpExtTCPRetransFail 843 0.0 >> hostname TcpExtTCPRcvCoalesce 949068035 0.0 >> hostname TcpExtTCPOFOQueue 470118 0.0 >> hostname TcpExtTCPOFODrop 9915 0.0 >> hostname TcpExtTCPOFOMerge 9 0.0 >> hostname TcpExtTCPChallengeACK 90 0.0 >> hostname TcpExtTCPSYNChallenge 3 0.0 >> hostname TcpExtTCPFastOpenActive 2089 0.0 >> hostname TcpExtTCPSpuriousRtxHostQueues 896596 0.0 >> hostname TcpExtTCPAutoCorking 547386735 0.0 >> hostname TcpExtTCPFromZeroWindowAdv 28757 0.0 >> hostname TcpExtTCPToZeroWindowAdv 28761 0.0 >> hostname TcpExtTCPWantZeroWindowAdv 322431 0.0 >> hostname TcpExtTCPSynRetrans 3026 0.0 >> hostname TcpExtTCPOrigDataSent 40976870977 0.0 >> hostname TcpExtTCPHystartTrainDetect 453920 0.0 >> hostname TcpExtTCPHystartTrainCwnd 11586273 0.0 >> hostname TcpExtTCPHystartDelayDetect 10943 0.0 >> hostname TcpExtTCPHystartDelayCwnd 763554 0.0 >> hostname TcpExtTCPACKSkippedPAWS 30 0.0 >> hostname TcpExtTCPACKSkippedSeq 218 0.0 >> hostname TcpExtTCPWinProbe 2408 0.0 >> hostname TcpExtTCPKeepAlive 213768 0.0 >> hostname TcpExtTCPMTUPFail 69 0.0 >> hostname TcpExtTCPMTUPSuccess 8811 0.0 >> >> Thanks!